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With a single exception among 11 strains, each strain of Y. enterocolitica representing one of the six O-groups possesses, as judged by the sugar composition of its lipopolysaccharides, a particular chemotype. All 14 of the strains examined possessed glucosamine, KDO, two heptoses and glucose. In the most complicated chemotype 10 sugars were demonstrable. Of three Y. enterocolitica strains not included in the 6 O-groups, two had the same chemotype as the representatives of the O-groups IV and VI. Details can be seen in the two tables.

D-3-Dodecanoyltetradecanoic acid has been separated from the lipid A of Yersinia pseudotuberculosis and its structure has been established by chromato-mass-spectrometry and 13C NMR spectroscopy, by comparison with authentic samples.

The chemical properties and the general biological activities of lipopolysaccharide (LPS) and Boivin-type endotoxin obtained respectively by phenol-water and trichloroacetic acid extraction from Yersinia enterocolitica serotypes O3 and O9 were studied. The yield of LPS from the O9 strain was about 10% of the O3 strain possibly because of the lower solubility of O9-LPS in aqueous phase. However, the chemical composition of O9-LPS was similar to that of O3-LPS in the proportions of reducing sugar, glucosamine, heptose, KDO, and lipid A. In pyrogenicity and local Shwartzman reactivity in rabbits and lethality for mice, there was also no difference between O3 and O9-LPS. The anthrone-positive carbohydrate and lipid A contents of Boivin-type endotoxin from O3 were higher than those of the endotoxin from O9. The biological activities of Boivin-type endotoxin from O3 were also remarkably higher than those of the endotoxin from O9. It seems that endotoxin of Y. enterocolitica serotype O3 may play an important role in infection by this organism.

The fine structure of isolated lipopolysaccharides (LPS) from the rough and smooth form of an Yersinia enterocolitica strain (Ye 75 R/Ye 75 S) and from smooth forms of Salmonella typhimurium (S 1010) and Escherichia coli (Essen) were examined electron-microscopically by negative staining. Partial denaturation of LPS in Tris-buffer with acid and/or polymyxin B treatment revealed a common structure of strandlike LPS. Electron-microscopically, LPS-strands were found to consist of two identical sub-strands which form a double helix. High resolution electron microscopy permitted the identification of a total of four longitudinal fibrils (diameter approximately 20 A); therefore, each sub-strand consists of two longitudinal fibrils. These results were correlated with those obtained with positive staining procedure and chemical fixation technique. The development of the "double-track"-profile of the outer membrane was interpreted to result from the projection of the helical longitudinal fibrils into the image plane.